14 DAY TRIAL // From a commodity one hundred years ago, today water has turned into a must. But in densely populated dry areas, the obvious solution is to get drinking water from the sea. People have been obsessed for millennia with finding a way to get rid of the sea salt for achieving usable water. But so far, the costs of desalination have proven prohibitive.
"Until recently, seawater desalination was a very expensive water source solution," said Gary Crisp, an engineer for the Water Corporation of Western Australia.
If you drink salt water, the body in fact loses more water, as it is used for expelling the extra-salt.
Seawater contains about 34.3 grams of salt per liter (paradoxically, seas near desert areas, where desalination is even more stringent, like Red Sea, or Persian Gulf, have higher salt concentrations). Desalination decreases salt levels to under 0.5 g/l, the limit for safe human consumption. Today, 40 to 50 billion liters of water are desalinated worldwide daily, representing roughly 0.2 % of the world's water consumption, but the tendency is rising.
"There is significant growth in desalination capacity throughout the world, and it is anticipated to continue for sometime," said Stephen Gray of Victoria University, who leads a new research program in Australia (where many areas experience severe droughts) aimed to make desalination costly-effective.
In the 4th century B.C., Aristotle was the first to come up with the concept of successive filters to remove the salt from seawater. But the first desalination process, employed by sailors in the second century on their ships, meant collecting the freshwater Steam from boiling saltwater. Due to the high energy consumption, this could not be made on a large scale. Even today, the "thermal desalination" is viable only in oil-rich, desertic countries in the Middle East.
Since the 1950s, salt filtering membranes, following the Aristotle concept, were developed. The membrane technique ("reverse osmosis") now needs just 25 % of the energy and 50 % of the costs of the thermal method.
"In the last ten years, seawater reverse-osmosis has matured into a viable alternative to thermal desalination," said Crisp. Still, large energy quantities are required to induce the high pressure that pushes the water through the filter, at the consumption of 14 kilowatt-hours to get 3,800 liters of desalinated seawater.
In US, the consumption per capita is 300-380 liters of water daily and the entire nation requires 1,220 billion liters daily of surface water and another 320 billion liters of ground water. If 50 % of this water came from desalination, US would have to built over 100 extra electric power plants, each of a gigawatt capacity. Currently 1,000 liters of desalinated seawater can cost about $ 0.8-1.05.
It may look cheap, but it is still cheaper in most areas to pump water out of the ground or bring it from outside. This is cost-effective only in regions affected by severe droughts. The issue is aggravated by the global warming and the water use increasing twice faster than population growth, making more and more communities to experience water shortages. This will increase the prices for freshwater, turning desalination increasingly attractive.
Worldwide there are over 15,000 desalination plants and there are efforts to make them more affordable.
Nine major Australian universities have joined efforts on the research for a membrane that would decrease desalination energy costs, as well as maintenance costs linked to gunk sticking to membranes and fouling them up.
"Lowering the energy required for desalination and the fouling propensity of membranes are the two biggest challenges facing desalination," said Gray.
New types of membrane materials would solve the problems and would drop to half the energy consumed for desalination. "We would hope to have something available within the next 10 years," Gray said.